Use of detoxified MSWI fly ash for cement stabilized macadam mixture: mechanism, mechanical and environmental considerations

In order to realize the recovery and stabilization of detoxified municipal solid waste incineration fly ash (DIFA) in roadbases, the synergetic hydration behavior of cement DIFA composite system and the mechanism of DIFA on the development of compressive strength of cement-stabilized macadam were investigated by means of macro-mechanical properties and microscopic characterizations of SEM, and the water stability, frost resistance and heavy metals’ leaching toxicity were also studied. Results showed that the compressive strength of cement-stabilized macadam increased first and then decreased with the increase of DIFA substitution percentage. The soluble chlorides introduced by DIFA were the key factors that affect the amount of hydration products and the development of macro-mechanical properties. The reasonable content of soluble chlorides not only accelerated the hydration of cement, but also produced a new product Friedel's salt, which made the structure more compact and optimized, and the macro-mechanical properties increased. However, when the substitution percentage of DIFA was high, the free chlorine appeared, forming a coating layer on the surface of cement particles, which hindered the further cement hydration and the development of macro-mechanical properties. The water stability of cement-stabilized macadam was improved by adding suitable DIFA, and the frost resistance was decreased, but it still met the technical requirements. The heavy metals in DIFA were firmly solidified in cement-stabilized macadam, and the leaching concentration was greatly reduced, thus realizing the stabilization and clean utilization of DIFA.